These were probably some of the last foot warmers of this style that were on the market. They were made by a company called Moira Pottery which operated from 1922-1972. I'm not sure when they started putting the reproduction ads on their wares, I usually associate that with the 1970s but Moira was clearly doing it ealier than that based on their dates of operation and how much of their pottery has them. It looks like Moira was part of a period in pottery where they were transitioning from the traditional utilitarian wares to nostalgic home decor, but clearly with the same techniques and designs that they had been using for everyday products in earlier decades. I wonder if, in the case of something like this, they realized that more people were buying ceramic foot warmers for use in decor than for actual foot warming, and decided to embellish the design with the fanciful transfer printing. It's so consistent with the foot warmers from the early-mid 20th century that it doesn't seem like it should qualify as a reproduction otherwise.